Surprised that no one has even suggested using a McIntosh cable when you are using McIntosh equipment. I use a pair of cables from McIntosh to alleviate some perceived brightness between my preamp and amp. They are readily available on Crutchfield and carry a 60-day return policy, so there is no risk. Right in your wheelhouse at $600.
Similarly, I use a Rega phono cable for my Rega P6. For me, if a mfg green lights a particular cable to use for their equipment, it makes sense to take advantage of it as there will be no surprises. You are simply engaging in the sound that the mfg has touted.
In addition, I purchased the McIntosh RCA's a few years ago and they are still priced the same. Ala their equipment, their cables also keep their value, which further reduces risk.